The present invention relates to transseptal catheterization, and more specifically relates to a needle assembly for transseptal catheterization.
The human heart contains four chambers: the right atrium, the right ventricle, the left atrium, and the left ventricle. The right atrium is in fluid contact with the superior vena cava (SVC) and the inferior vena cava (IVC). The right atrium is separated from the right ventricle by the tricuspid valve, while the left atrium is separated from the left ventricle by the mitral valve. The right atrium and left atrium are separated by the interatrial septum, while the right ventricle and left ventricle are separated by the interventricular septum.
There are a multitude of therapeutic and diagnostic procedures in which a catheter is passed within a guide sheath or over a guide wire to access the chambers of the heart. The right atrium can be accessed from the superior vena cava or inferior vena cava. The right ventricle can be accessed from the right atrium. The left ventricle can be accessed from the aorta. The left atrium can be accessed directly from the left ventricle (through the mitral valve); however, such an approach is a relatively difficult maneuver due in part to the tortuous path that must be navigated with the catheter. Such a maneuver is problematic for various reasons, including a bleeding risk and a clotting risk to the patient (because it is the arterial side, it has a relatively high pressure, which exacerbates such risks). In addition, this approach may cause arrhythmias. Therefore, another approach for accessing the left atrium was developed. In this approach, a small hole is placed in the interatrial septum, so that the left atrium can be accessed from the right atrium. This hole is typically created by a needle puncture and is referred to as transseptal catheterization.
In the standard transseptal catheterization procedure, three main, separate tools are involved: a sheath with a sheath hub, a dilator with a dilator hub, and a needle assembly including a cannula, a needle hub and a stylet. The stylet is usually a small, guidewire-like device that is threaded through the needle cannula and attaches to the needle hub proximally. The distal tip of the stylet extends beyond the distal tip of the needle. The distal section of the needle has a shoulder or tapered section that corresponds with an internal taper at the distal tip of the dilator. When the needle is fully inserted into the dilator, the needle shoulder functions as a hard stop that limits the distance that the tip of the needle can exit from the dilator.
The typical transseptal procedure entails numerous steps. First, right femoral vein access is gained via the Seldinger technique. Second, a guidewire is passed through an introducer sheath, which was placed in the first step, into the femoral vein and threaded up the IVC to the SVC. Third, a sheath and dilator assembly is maneuvered to the SVC by being passed over the guidewire. Fourth, the guidewire is removed. Fifth, the needle assembly, usually including the stylet, is advanced through the inner lumen of the dilator until the distal tip of the needle (or stylet) is just proximal of the distal tip of the dilator. Sixth, the stylet, if present, is removed, and the needle is advanced until the tip of the needle is just proximal of the distal tip of the dilator. Seventh, the dilator/sheath/needle assembly is pulled caudally until the distal tip of the dilator is just resting on the fossa ovalis, which is a relatively thin area in the interatrial septum. Eighth, the needle is advanced forward through the dilator to puncture the septal wall (fossa ovalis). Ninth, and finally, the sheath and dilator assembly is fed through the septal wall over the needle, thereby gaining access to the left atrium.
One risk associated with transseptal needle use is inadvertent exposure. The sheath/dilator assembly and transseptal needle assembly are usually not interlocking Thus, the needle assembly can freely translate and rotate within the sheath/dilator assembly. This freedom of movement means that the position of the needle assembly in relation to the sheath/dilator assembly must be manually maintained by the user. In particular, during the needle insertion step and the subsequent navigation of the tip of the sheath/dilator/needle assembly to the fossa ovalis, if the translational position of the needle assembly is not controlled or monitored, there is a risk of inadvertent exposure of the stylet and/or needle tip The maintenance of needle position in relation to the dilator is especially challenging for inexperienced users. Inadvertent exposure can result in damage to the vascular and cardiac walls, which could further result in generation of potentially dangerous emboli.
In the standard transseptal procedure, in order to mitigate this risk, the physician performs a measurement ex vivo to determine the point at which the stylet and/or needle tip is unexposed and just proximal of the dilator tip. To do this, the physician first inserts the needle fully into the dilator so that the stylet and/or needle tip exits the dilator. Next, the physician withdraws the needle proximally so that the stylet and/or needle tip is no longer exposed. At this point, the physician measures how far the needle handle is proximally offset from the dilator hub. Generally, this offset distance is “two-finger-widths” if the stylet is connected to the needle and “one-finger-width” if the stylet has been removed. This is an imprecise and non-standardized measurement that adds an extra step to the procedure. In addition, when the needle is inserted into the dilator/sheath assembly, which has been placed previously in vivo and in the SVC, the physician has to take care so that the needle does not advance beyond the offset distance(s) that had been previously measured.
A second risk is the inadvertent puncture of adjacent structures rather than the fossa ovalis. These adjacent structures include: the aortic root, the coronary sinus, and the posterior free wall of the right atrium. If perforation is limited to just the needle, the result is usually benign. However, if the dilator/sheath assembly is advanced over the needle into the aortic root or pericardium, complications, such as cardiac tamponade, can occur.
In the standard transseptal procedure, in order to mitigate this risk, the physician uses adjunctive techniques and technology to locate the transseptal tools relative to the pertinent intracardiac structures, especially the fossa ovalis. These adjunctive techniques and technology comprise one or any combination of the following: biplane fluoroscopy; use of a pig-tailed catheter to identify the aortic root; pressure manometry to identify aortic/right atrial and left atrial pressures; contrast infusion; and transesophageal (TEE) and intracardiac (ICE) echocardiography.
A third risk is the generation of particulates as the needle is advanced through the dilator. During this needle advancement, the tip of the needle has the potential to skive the inner surface of the dilator, especially at the tapered tip section. Since the needle and dilator are advanced into the left atrium, one of these particulates could be released and travel from the left atrium directly to the carotid or coronary arteries. The particulate could then, if large enough, block one of the arteries, resulting in a stroke or myocardial infarction. In the standard transseptal procedure, in order to mitigate this risk, the needle and dilator assembly are flushed after the ex vivo measurement step. In addition, the purpose of the stylet, which is re-attached to the needle after the flushing step, is to act as a guidewire and prevent the tip of the needle from skiving the dilator inner surface during needle advancement through the dilator.
A fourth risk is the generation of air emboli during the puncture procedure. There is no seal between the needle cannula and the dilator hub at the proximal end of the needle/dilator/sheath assembly. This creates a potential path for air to travel into the patient's heart, which can result in the formation of an air embolism. This is particularly risky if the air exits the distal tip of the dilator while it is in the left atrium; an air embolism in the left atrium can travel directly to the brain and cause a cerebral ischemic event.